We recently moved into this home built in 1870. It appears the shingles were put right into the planks (currently no plywood).

Our budget is limited and adding plywood will set us back 5K (never mind the shingles/labor). One roofer went as far to say that he wouldn’t do the job without putting on the plywood as it would void the warranty.

If the existing decking is Skip Sheathing, which is either equal 1" x 6" or any other regular dimensional lumber or a haphazard conglomeration of all sorts of sized boards, and they have at least a 1" gap present between the boards, spacing the board decking apart from each other, then YES, you will need to overlay the existing decking with new plywood.

The spaced board skip sheathing method was intentionally used for Cedar Shingle applications, so that the underside of the Cedar Shingle roof could be breathable, keeping the Cedar dry from continuous air flow.

If you say that there a “Regular” asphalt composition shingles installed currently on top of the decking, then if there were gaps between the boards, they may have installed smaller pieces of something like 1" x 2" boards to solidify the deck. If that is the case, then you would probably NOT need to overlay the decking with new plywood sheathing.

Are there any spaces between the boards and if so, how great of a gab is typical throughout?

Apart from two small areas still with cedar shakes, the majority of the home does in fact have asphalt shingles on already.

I don’t believe there are any smaller boards used on top of the planks…and the planks are pretty tight (probably less then 1’’ apart).

Since the asphalt is already on…does that mean it’s probably safe for me to go the same route while re-roofing? Or were the previous owners just lazy?

Thanks.[/quote]

I did not mean to imply that the smaller boards would be “On Top” of the existing planks. The thinner boards would have possibly been used to “Fill In” the gaps between the old planks.

It sounds like, from your description, that the gaps are small enough to be able to remove the old roof and apply new composition shingles directly on top of the existing decking, without having to overlay the old decking plank boards with new plywood sheathing.

You might want to see if a local building inspector could come out prior to beginning the contract and verify if he feels that new sheathing overlay is required.

I prefer to tear off the old shingles. If you are thinking of Re-Roofing over the top of the existing ones, that is a very poor choice and will come back to bite you in the azz in a short time. Reroofs do not last as long, typically, as a proper new installation does, due to heat sumps trapped in between the multiple layers of shingles. This trapped heat and moisture decays the new surface shingles prematurely and also is not typically covered under the fine print of the shingle manufacturers warranty exclusions.

if the home is that old, it has had many roofs on and off again and again. The existing planks may have ckecks and split, and if there are large gaps, you cannot nail in the designated nailing area to conform to manufactures warrenty. The roofer is covering his az by recomeneding the sheet over planks. I almost always sheet over planks so I can nail on the line…OSB is a less expensive choice if budget is a problem. about 1/3 the cost of plywood…